Probably the biggest miss of the franchise was avoiding the titular "Fantastic Beasts" after the first movie. Plus the whole, bringing muggles into the fold - that's the kind of not-Harry content/world building that could have had legs.
But the went all, "Look! It's just like Voldemort!" And, "That's Dumbledore's brother or something - you remember Dumbledore, right?"
Why is it so hard to do magical Steve Irwin going around the Wizarding World looking for fantastical beasts instead of... whatever these movies are now?
Not every movie has to be about some high stake world ending menace; keep it simple, keep it fun, and people would want to watch it.